Shift Of Phase Transition Temperature Research Articles

Unveiling the Monoclinic Phase in CsPbBr3-xClx Perovskite Crystals, Phase Transition Suppression and High Energy Resolution γ-Ray Detection.

All-inorganic CsPbBr3 and CsPbCl3 perovskites are promising materials for high-performance solar cells and advanced radiation detection technologies with high stability. Here we report that CsPbBr3-xClx (x = 0-3) crystals exhibit eutectoid behavior for the melting points and phase transition temperatures. The well-known halide perovskite cubic phase transition temperature shifts near room temperature (∼37 °C for CsPbBr2Cl). We conducted an extensive crystallographic analysis on single crystals of 7 different compositions, including the end members CsPbBr3 and CsPbCl3. Contrary to previous beliefs, we discovered they exhibit a monoclinic structure with space group symmetry P21/m at room temperature, rather than the orthorhombic Pnma. This new structural model is more precise and features a unit cell volume that is four times larger than that of the orthorhombic model. From high-quality single crystals of CsPbBr2Cl, grown by the Bridgman method, we constructed γ-ray detectors achieving an energy resolution of 7.2% at 200 V for 57Co radiation. Thermally stimulated current spectroscopy of the CsPbBr2Cl samples revealed that the defect densities in crystals from different regions of the ingot were relatively uniform, with values of ∼4.72 × 1012 and ∼5.09 × 1012 cm-3. These findings indicate that low deep-level defect densities can be achieved that are consistent with the notable performance of the CsPbBr2Cl perovskite as a high-energy γ radiation detector.

Super soft poly(N-isopropylacrylamide) microgels using functionalized starch nanoparticles as crosslinker

A set of poly(N-isopropylacrylamide) p(NIPAM) microgels was successfully prepared through precipitation polymerization (PP) using acryloyl starch nanoparticles (ASNPs) as crosslinkers. Functionalized starch nanoparticles used in microgel preparation, with a degree of substitution (DS) of 0.78 (ASNP12) or 1.37 (ASNP24) were found to have different properties. Dynamic light scattering (DLS) revealed that microgels prepared with ASNP12 exhibit a higher swelling capacity compared to the microgels designed with ASNP24, which was also observed by atomic force microscopy (AFM), showing super soft microgels flattened into disk shape on the substrate. This may be related to softer and surface smoothed microgels. Turbidity analysis revealed a slight shift of the so-called volume phase transition temperature (VPTT) towards higher values for microgels synthesized with ASNP24, indicating its contribution as a hydrophilic comonomer. Considering their high swelling capacity, these bio-based crosslinked microgels are potential materials for adsorptive processes. They can also be considered as candidates for biomedical applications due to the presence of a biopolymer in their structure.

The Role of Diamonds Dispersed in Ferronematic Liquid Crystals on Structural Properties

A study of the role of diamond nanoparticles on 5CB liquid crystal composites with Fe3O4 nanoparticles is presented. Composite ferronematic systems based on the nematic liquid crystal 5CB doped with Fe3O4 magnetic nanoparticles and additionally bound to diamond nanoparticles (DNPs), of a volume concentration of 3.2 mg/mL, 1.6 mg/mL and 0.32 mg/mL, were investigated using both magneto-optical effect and surface acoustic waves (SAWs) to study the role of diamond nanoparticles on the structural properties of ferronematic liquid crystals. The responses of light transmission and SAW attenuation to an external magnetic field were investigated experimentally under a linearly increasing and decreasing magnetic field, respectively. Investigations of the phase transition temperature shift of individual composites were also performed. The experimental results highlighted a decrease in the threshold field in the ferronematic LC composites compared to the pure 5CB as well as its further decrease after mixing Fe3O4 with diamond powder. Concerning the transition temperature, its increase with an increase in the volume fraction of both kinds of nanoparticles was registered. The role of diamond nanoparticles in the structural changes and the large residual light transition and/or attenuation (memory effect) were also observed. The presented results confirmed the potential of diamond nanoparticles in nematic composites to modify their properties which could lead to final applications.

Enhanced electrocaloric effect in Sr-doped Ba0.85Ca0.15Zr0.1Ti0.9O3 lead-free thin films near room temperature

Ferroelectric thin films with giant room-temperature electrocaloric effect (ECE) could be very useful in design of solid-state refrigeration devices. Here, lead-free Ba0.85Ca0.15-xSrxZr0.1Ti0.9O3 (BCZT-xSr, 0.01 ≤ x ≤ 0.10) thin films are successfully prepared on the substrates (Pt/Ti/SiO2/Si) via sol-gel route, and the effect of the Sr substitution on the structure, electric properties and ECE of the films were investigated. The dielectric analyses show that the rhombohedral-tetragonal phase transition temperature (TR-T) move to a higher temperature and the tetragonal-cubic phase transition temperature (Tm) shift to a lower temperature with increasing Sr content, and finally the TR-T peaks merge into the Tm peaks at room temperature. The BCZT-0.05Sr film presents a giant ECE with ΔT = 27.1 K and ΔS = 30.6 J K−1 kg−1 at 800 kV cm-1 near room temperature (301 K). The giant ΔT benefits from a multiphase coexisting region with successive R-T and T-C phase transition character near room temperature. These results indicate that the lead-free Sr-doped BCZT thin film is an attractive material for application in ECE refrigeration devices.

Photoinduced Mechanical Cloaking of Diarylethene-Crosslinked Microgels.

The serial connection of multiple stimuli-responses in polymer architectures enables the logically conjunctive gating of functional material processes on demand. Here, a photoswitchable diarylethene (DAE) acts as a crosslinker in poly(N-vinylcaprolactam) microgels and allows the light-induced shift of the volume phase-transition temperature (VPTT). While swollen microgels below the VPTT are susceptible to force and undergo breakage-aggregation processes, collapsed microgels above the VPTT stay intact in mechanical fields induced by ultrasonication. Within a VPTT shift regime, photoswitching of the DAE transfers microgels from the swollen to the collapsed state and thereby gates their response to force as demonstrated by the light-gated activation of an embedded fluorogenic mechanophore. This photoinduced mechanical cloaking system operates on the polymer topology level and is thereby principally universally applicable.

Effect of Magnetic Field and Hydrostatic Pressure on Metamagnetic Isostructural Phase Transition and Multicaloric Response of Fe49Rh51 Alloy

The effect of a high magnetic field up to 12 T and a high hydrostatic pressure up to 12 kbar on the stability of the metamagnetic isostructural phase transition and the multicaloric effect of Fe49Rh51 alloy has been studied. The phase transition temperature shifts under the magnetic field and the hydrostatic pressure on with the rates of dTm/μ0dH = −9.2 K/T and dTm/dP = 3.4 K/kbar, respectively. The magnetocaloric and multicaloric (under two external fields) effects were studied via indirect method using Maxwell relations. The maximum of the entropy change is increasing toward the high temperature region from ∆S~2.5 J/(kg K) at 305 K to ∆S~2.7 J/(kg K) at 344 K under simultaneously applied magnetic field of 0.97 T and hydrostatic pressure of 12 kbar. The obtained results were explained using the first-principle calculations of Gibbs energies and the phonon spectra of the ferromagnetic and the antiferromagnetic phases. Taking into account the low concentration of antisite defects in the calculation cells allows us to reproduce the experimental dTm/dP coefficient.

Phosphatidylinositol phase behavior in symmetric and asymmetric model membranes.

Phosphatidylinositol (PI) is a precursor to phosphoinositides (PIPs) which are important cellular signaling molecules. While the phase behavior of PI in simple model membranes has been investigated, little is known about its phase behavior in the presence of PIPs. Furthermore, the effect of divalent cations on PI/PIP interaction has not been detailed. Determining PI/PIP phase behavior is of physiological relevance because it potentially affects the lateral distribution of PIPs in cellular membranes and hence the spatiotemporal control of protein function. For diplamitoylphosphatidylinositol (DPPI) we find in pH 7.2 buffer a phase transition temperature of 43.6°C, while in the presence of Ca2+ and Mg2+ the phase transition temperature shifts to 55.8°C and 51.6°C, respectively. In addition, we investigate divalent cation dependent PI/PI(4,5)P2 phase behavior. To study PI phase behavior in asymmetric lipid bilayers, we fabricate asymmetric giant unilamellar vesicles (aGUVs) using the hemifusion method. We describe the conditions to obtain aGUVS with PI in the outer leaflet and characterize their domain morphology.

57Fe Mössbauer spectroscopy and high-pressure structural analysis for the mechanism of pressure-induced unique magnetic behaviour in (cation)[FeIIFeIII(dto)3] (cation = Ph4P and nPrPh3P; dto = 1,2-dithiooxalato).

A mixed-valence iron(II,III) coordination polymer, (Ph4P)[FeIIFeIII(dto)3] (2; Ph4P = tetraphenylphosphonium, dto = 1,2-dithiooxalato), exhibits a thermal hysteresis loop and a low temperature shift of the ferromagnetic phase transition temperature, with increasing pressure. The latter magnetic behaviour can also be observed in a novel compound (nPrPh3P)[FeIIFeIII(dto)3] (3; nPrPh3P = n-propyltriphenylphosphonium). To understand the structural information under pressure, we performed high-pressure powder X-ray diffraction, and the result suggests that there was no structural phase transition for either compound. Considering the 57Fe Mössbauer spectroscopy studies, both 2 and 3 may have a high transition entropy, and this finding is caused by pressure-induced unique magnetic behaviours.

Mechanical stability of (Li,Na,K)NbO3-based multilayered piezoceramics with Ag/Pd inner electrodes

Lead-free (Li,Na,K)NbO3-based multilayered piezoceramics with Ag0.9Pd0.1 inner electrodes were prepared, and their large-signal piezoelectric properties under combined electrical and mechanical loadings were characterized at room temperature. The piezoelectric constant d33∗(=SMax/EMax) of the multilayer was 96 pm/V with an applied unipolar field of 5 kV/mm under zero stress. More importantly, a favorable stress stability of d33∗ was observed, with a slight variation ≤8% of SMax, when the uniaxial stress was increased from −5 to −80 MPa. Further investigations of temperature-dependent x-ray diffraction, permittivity, and an energy-dispersive x-ray spectrometer revealed that the mechanical stability of d33∗ was due to a shift in phase transition temperature caused by a solid solution of the Ag inner electrode to the A-site of (Li,Na,K)NbO3 piezoceramics.

Piezoelectricity of Sm-doped Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystals by enhancement of local disorder polarization

Relaxor-based ferroelectrics are a kind of ideal material, which are widely applied in transducers, medical ultrasound probes, sensors and a series of electromechanical instruments. Rare dopants can enhance the piezoresponse by introducing local structural heterogeneity. However, the origination of the giant piezoresponse is still controversial due that the instability of polarization results from the shift of phase transition temperature and component inconsistency. Herein, we grew high homogeneity Sm-doped Pb(Zn1/3Nb2/3)O3–5%PbTiO3 (Sm-PZNT) single crystals, which the d33 values is of ∼3200 pC/N and variation of phase transition temperatures is less than 7 K. The local polarization is characterized by atomic-scale level transmission microscopy (HRTEM). The macro-irregular ferroelectric domain is observed by piezoforce microscopy (PFM). These results identify that the Sm3+ dopant enhances the local structural heterogeneity and improves the piezoelectric properties of PZNT with slightly effect on phase transition temperatures. These results pave the way towards a new generation of high-performance relaxor ferroelectrics design.

Influence of stress on the electromechanical properties and the phase transitions of lead-free (1 − x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3

The influence of stress on the phase boundaries of polycrystalline lead-free perovskite (1 − x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 (x = 0.4, 0.5, and 0.6) was characterized through the temperature- and stress-dependent small-signal dielectric and piezoelectric response from − 150 to 200 °C under uniaxial compressive stress up to − 75 MPa. For all three compositions, the phase transition temperatures separating the rhombohedral, orthorhombic, tetragonal, and cubic phases were shifted to higher temperatures with an increase in the uniaxial mechanical loading, corresponding to a significant decrease in the dielectric and piezoelectric responses. Additional stress-dependent relative permittivity measurements up to − 260 MPa were conducted at four different constant temperatures (− 10, 10, 25, and 40 °C), revealing significant increases in the dielectric response, making these materials interesting for tunable dielectric applications. Furthermore, the stress-induced shift in phase transition temperatures was confirmed by in situ combined temperature- and stress-dependent Raman spectroscopy measurements under different constant uniaxial loads within the temperature range from 30 to 130 °C.Graphical abstract

Impedance and modulus spectroscopic studies of lead free Na[formula omitted]Dy[formula omitted]TiO3 Ceramic

A lead-free perovskite ceramic, Na12Dy12TiO3 (NDT), was synthesized via the conventional solid state reaction method. The sample’s structural, microstructural, and electrical characterizations were performed over the varying range of frequency and temperature. The detailed electrical behavior of the samples has been analyzed and explored by applying impedance spectroscopy. The structural study confirmed the orthorhombic structure of NDT material, with the presence of a very small contribution of the impure pyrochlore phase. The dielectric permittivity of the sample as a function of temperature shows the ferroelectric to paraelectric phase transition temperature to be ∼94 °C, and the shift of phase transition temperature is attributed to its structure. The frequency and temperature-dependent electrical features are studied within the framework of impedance, modulus, and conductivity spectra. The Nyquist plots detect the contribution of grain/grain boundaries to the inclusive polarizations. The presence of two depressed semicircular arcs in the Nyquist Plots (both grain/grain boundaries contribute to electrical properties) was approached for higher temperatures (≥350 °C), suggesting the relaxation phenomena to be temperature dependent with a distribution of relaxation times. Also, the modulus spectra analysis confirms the temperature-dependent multiple relaxation phenomena to be of the Non-Debye type and is present in the sample at ≥350 °C. The conductivity spectra confirm the presence of dc conduction at ≥350 °C and a temperature-dependent polaron hoping conduction behavior with the validity of Johnscher’s universal law.

Calculation and discussion of the distribution of double magnetic ions in the lattice site: The perovskite structure with d3 -d5 superexchange interaction

In this paper, for the d3-d5 superexchange perovskite system, the distribution of double magnetic ions in the B-site is quantitatively calculated using molecular field theory. The model we established, which applies to RFe1−pCrpO3, goes one step further than the former anti-site defect one. Calculations have revealed that the distribution of Fe and Cr ions in many previous studies of Fe–Cr perovskite does not always conform to the uniform distribution. Instead, they exhibit an effect that aviods the Fe–Fe or Cr–Cr clustering. This work settles previous disputes regarding the phase transition temperature range of double perovskites and explains why the phase transition temperature shifts with the same given doping proportion. It furnishes theoretical guidance for the design of functional materials with arbitrary phase transition temperatures.

Cu2+ tunable temperature-responsive Pickering foams stabilized by poly (N-isopropylacrylamide-co-vinyl imidazole) microgel: Significance for Cu2+ recovery via flotation

Froth flotation has been a key chemical process extensively used in the recovery of heavy metal ions (e.g. Cu2+) from contaminated water, while often criticized by a secondary pollution of the added collectors, and a less selectivity to specific ions since the ion removal by particles is independent from the post-step of particle flotation. To facilitate the industrial operation, a “smart” flotation with foams responsively stabilized after selective adsorption of target ions from competitive ions are highly desired. In the current study, “smart” foams stabilized by Cu2+ responsive microgels were presented as a proof-of-concept.Firstly, a Cu2+-responsive thermo-sensitive poly (N-Isopropylacrylamide-co-Vinyl imidazole) (PNV) microgel with a hydrodynamic radius (Rh) ∼ 334 nm and a fuzziness ∼ 37.2 nm was synthesized. Cu2+-imidazole complexation was demonstrated to enhance the microgel swelling with a softer and more homogenous microstructure, having the Rh increased by 30–50 nm for 0.005 M to 0.25 M Cu2+ and a significant volume phase transition temperature (VPTT) shift from ∼ 40 °C to ∼ 50 °C for 0.005 M Cu2+, ∼60 °C for 0.05 M Cu2+ and ≫ 60 °C for 0.25 M Cu2+.Secondly, temperature responsive foams with a ultra-stability below VPTT of the microgel and a rapid collapse above the VPTT were readily produced based on PNV microgels. Cu2+ complexation enabled a modulation of temperature responsiveness of the foams, able to maintain a good foam stability in high temperatures (e.g. a life time > 6 h at 45 °C for 0.25 M Cu2+) where foams rapidly collapsed for other cations (e.g. ∼ 2 min, ∼10 min and ∼ 15 min at 45 °C for Na+, Mg2+, Zn2+, respectively), showing significance for selective recovery of Cu2+ from competitive ions via flotation.Furthermore, an interfacial study at air–water interface revealed a better surface activity of Cu2+ -complexed PNV microgel with a less temperature dependence. An abrupt reduction of interfacial rheology around the VPTT with a G’s(25 °C)/G’s(70 °C) ratio ∼ 300.1 observed was believed to be the main reason of the responsive foam destabilization for PNV2, which was avoidable by entanglements between Cu2+-complexed PNV microgels, giving a G’s(25 °C)/G’s(70 °C) ratio ∼ 1.68. Ultimately, the good Cu2+ selectivity of PNV2 microgel was well demonstrated in mixed solutions of competitive ions Na+, Mg2+, Zn2+ in terms of Cu2+ sorption, particle swelling and foam stabillity. This study demonstrated a responsive Pickering foam stabilized by a Cu2+ tunable microgel, laying foundations to develop microgel-based flotation as a smart and green technology for Cu2+ recovery.

Biophysical Characterization of (DOX-NPtm): FTIR and DSC Studies

Doxorubicin loaded into liposomes grafted with polyethylene glycol (PEG) has been demonstrated to have a longer circulation time and lower cardiotoxicity than doxorubicin (DOX). This study aims to investigate the biophysical characterization of a marketed formulation DOX-encapsulated liposome (DOX-NPTM). The interactions between doxorubicin and liposomal lipids can help in liposomal development. The liposome and DOX-NPTM were characterized in terms of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The rheological properties of liposomal samples were also measured. Physical interactions may be occurred between the drug functional groups and liposomal lipids, probably by weak hydrogen bond formation or weak bond formation due to dipole-dipole interaction. There was no shift of existing peaks or appearance of new peaks was detected between the characteristic peaks of the liposomal lipids were present in the DOX-encapsulated liposome sample. This suggests that there were physical interactions that took place only between the drug and lipids and no chemical interaction between them. DSC information shows that the phase transition temperature shifts to lower temperature degrees after loading of DOX into the liposomes. The DSC curve has a small broadening. This may infer a little cooperativity decrease between acyl chains of liposomal membranes after DOX inclusion. The encapsulation of DOX into liposomes decreases the plastic viscosity of liposomes (from 1.64 to 1.48 cP), which shows that the membrane fluidity was increased.

Phase-field modelling of paramagnetic austenite–ferromagnetic martensite transformation coupled with mechanics and micromagnetics

A three-dimensional phase-field model is proposed for simulating the magnetic martensitic phase transformation. The model considers a paramagnetic cubic austenite to ferromagnetic tetragonal martensite transition, as it occurs in magnetic Heusler alloys like Ni2MnGa, and is based on a Landau 2-3-4 polynomial with temperature dependent coefficients. The paramagnetic–ferromagnetic transition is recaptured by interpolating the micromagnetic energy as a function of the order parameter for the ferroelastic domains. The model is numerically implemented in real space by finite element (FE) method. FE simulations in the martensitic state show that the model is capable to correctly recapture the ferroelastic and -magnetic microstructures, as well as the influence of external stimuli. Simulation results indicate that the paramagnetic austenite to ferromagnetic martensite transition shifts towards higher temperatures when a magnetic field or compressive stress is applied. The dependence of the phase transition temperature shift on the strength of the external stimulus is uncovered as well. Simulation of the phase transition in magnetocaloric materials is of high interest for the development of energy-efficient magnetocaloric cooling devices.

Deuteration triggered downward shift of dielectric phase transition temperature in a hydrogen-bonded molecular crystal

Deuteration of hydrogen-bonded phase transition crystals can increase the transition temperatures due to the isotope effect. But rare examples show the opposite trend that originates from the structural changes of the hydrogen bond, known as the geometric H/D isotope effect. Herein, we report an organic crystal, diethylammonium hydrogen 1,4-terephthalate, exhibits a reversible structural phase transition and dielectric switching. Structural study shows the cations reside in channels formed by one-dimensional hydrogen-bonded anionic chains and undergo an order-disorder transition at around 206 K. The deuterated counterpart shows an elongation of the O···O hydrogen bond by about 0.005 Å. This geometric isotope effect releases the internal pressure of the anionic host on the cation guests and results in a downward shift of the phase transition temperature by 10 K.

The influence of non-stationarity and interphase curvature on the growth dynamics of spherical crystals in a metastable liquid

This manuscript is concerned with the theory of nucleation and evolution of a polydisperse ensemble of crystals in metastable liquids during the intermediate stage of a phase transformation process. A generalized growth rate of individual crystals is obtained with allowance for the effects of their non-stationary evolution in unsteady temperature (solute concentration) field and the phase transition temperature shift appearing due to the particle curvature (the Gibbs-Thomson effect) and atomic kinetics. A complete system of balance and kinetic equations determining the transient behaviour of the metastability degree and the particle-radius distribution function is analytically solved in a parametric form. The coefficient of mutual Brownian diffusion in the Fokker-Planck equation is considered in a generalized form defined by an Einstein relation. It is shown that the effects under consideration substantially change the desupercooling/desupersaturation dynamics and the transient behaviour of the particle-size distribution function. The asymptotic state of the distribution function (its 'tail'), which determines the relaxation dynamics of the concluding (Ostwald ripening) stage of a phase transformation process, is derived. This article is part of the theme issue 'Transport phenomena in complex systems (part 1)'.

Core-Shell Structure and Dielectric Properties of Ba0.6Sr0.4TiO3@ Fe2O3 Ceramics Prepared by Co-Precipitation Method

Ba0.6Sr0.4TiO3 (BST) ceramic materials have been widely used in the field of multilayer ceramic capacitors. Surface modification through the surface coating to form a heterogeneous layer could effectively improve the dielectric properties. In this work, BST powders were prepared by a co-precipitation method. The effects of reaction conditions on the microstructure of the BST powder were investigated. The reaction temperatures significantly affected the morphology of BST powder, and the rhombic-type particles were obtained with the reaction temperature around 80 °C. Meanwhile, the BST@Fe2O3 was prepared by the chemical precipitation method using BST powders with rhombic-type microstructure as “core”, and the so-called “core-shell” microstructure was confirmed in the BST@Fe2O3 powder. Then, BST@x wt%Fe2O3 (x = 2.5, 5, 7.5, and 10, denoting the different content of Fe2O3) ceramics were further prepared, and the influence of “core-shell” structure on the phase structure, microstructure, and dielectric properties was investigated. With the increasing of Fe2O3 content, the ferroelectric–paraelectric phase transition temperature shifts toward lower temperatures, and dielectric peaks gradually become broad and frequency-dependent, which may be due to inconsistent chemical composition from core to shell.

Effect of thermal profile on a shift in phase transition temperature of Sb-doped KNN piezoceramic

This work investigated the impact of the thermal profile in the shift of phase transition temperature for KNNS piezoceramic, using high-resolution synchrotron x-ray powder diffraction (SXPD) and dielectric measurement. The temperature-dependent dielectric permittivity and SXPD profile showed that all phase transformations occurred at higher temperature under heating than under cooling. Moreover, under cooling from 227 °C to −163 °C and reheating to 227 °C, none of the unit-cell volumes fully recovered to their initial size. These results suggest that the change in unit-cell volume under heating/cooling plays a significant role in the shift of phase transition temperatures that was observed.